1. Technical Field
The present invention relates to a test apparatus for testing a device under test such as a semiconductor circuit. The present invention further relates to a pin electronics card, an electric device, and a switch for use with such a test apparatus. In particular, the present invention relates to a test apparatus or the like that protects an internal circuit from a surge etc.
2. Related Art
One test apparatus for testing a device under test such as a semiconductor circuit is an apparatus equipped with a pin electronics card exchanging signals with a device under test. The pin electronics card includes an internal circuit (e.g. driver comparator), and a switch (i.e. relay) switching whether to connect the internal circuit to the input/output pin of the device under test.
The transmission characteristic of the switch becomes an issue when a test signal of a high frequency is inputted to a device under test. In view of this, the switch is preferably small, for shortening the length of the transmission line. One example of the switch is an MEMS (Micro Electro Mechanical System) switch utilizing the MEMS technology.
The MEMS switch is provided with a cantilever formed by attaching two kinds of metal plates having different thermal expansion coefficients from each other, and functions as a switch by switching whether to heat the cantilever by means of a heater of the like. One example of the MEMS switch is a bimetal switch of a “normally-off” type, which is turned OFF while not heated, and turned ON when heated.
The heater for heating the cantilever is supplied with a source power from the power source of the pin electronics card. While a source power is not supplied to the pin electronics card (e.g. in transportation of the pin electronics card), the switch is in the OFF state, and so the internal circuit is cut off from outside. For this reason, even when a surge is caused at the external terminal of the pin electronics card attributable to static electricity or the like, the surge is not conveyed to the internal circuit so that the internal circuit is protected. We have not recognized any related patent documents or the like, and so the description thereof is omitted here.
However if a bimetal switch of a normally-off type is left in the OFF state for a long time, or is repeated to be ON and OFF, the amount of curvature in the OFF state of the cantilever deteriorates. When the amount of curvature in the OFF state of the cantilever deteriorates, a problem arises that the cantilever is mistakenly in contact with the fixed contact.
Moreover, the amount of curvature in the OFF state of the cantilever fluctuates according to the change in ambient temperatures. Accordingly, the contact pressure between the cantilever and the fixed contact when controlled to the ON state also fluctuates according to the ambient temperatures. Since the switching life of the contact depends on the contact pressure, it is preferable to operate the contact within a predetermined range of contact pressures. However if the range of contact pressures is determined, the ambient temperature in which the contact is usable will be accordingly limited.
Moreover, a bimetal switch includes a package section that contains a cantilever and a fixed contact in an airtight manner. The package section is formed by anodic bonding the silicon substrates at the side surfaces to the glass substrates at the front and the back surfaces. The anodic bonding is performed by applying a high voltage in a high temperature of about 200-400 degrees centigrade. In manufacturing a bimetal switch of a normally-off type, the high voltage is applied when the cantilever is in contact with the fixed contact, by the high temperature applied in the anodic bonding. When a high voltage is applied when the cantilever and the fixed contact are in contact with each other, there will be caused a problem of “soft stick” that the cantilever and the fixed contact are bonded to each other. This leads to deterioration of yield in production of pin electronics card that utilize a bimetal switch of the normally-off type.